Transcript Evidence of the Past

Evolution
•Scientists believe that all living organisms on earth
share a common ancestor.
•Newer species arise from older species by evolution.
•Evolution is the process by which populations accumulate
inherited changes over many, many generations.
How does evolution happen?
Charles Darwin
________________, born in 1810,
is credited with the first theory explaining evolution.
Darwin observed that different species of birds were
uniquely adapted to their environment.
species
_____________ - a group of organisms that can mate
with one another to produce fertile offspring.
adaptation
_______________
– a characteristic that helps an organism
survive and reproduce in its environment
Sharper teeth to eat meat,
examples: ________________________________________
lungs to live on land, longer neck to reach food
________________________________________
He learned from plant and animal breeders.
They could select for desirable traits by picking what
animals will breed together.
He reasoned that this could happen in nature but it would
take MUCH longer.
He learned about populations.
Species can produce too many offspring but starvation,
disease, war, and predators limit the population size.
So there must be something special about the survivors—
they must inherit traits that help them survive in their environment.
Darwin proposed that evolution occurred by
natural selection
_____________________
acting on the adaptations
Darwin’s theory of Evolution by Natural Selection
the process by which organisms with favorable traits
survive and reproduce more than organisms without the
favorable trait.
overproduction
__________________more offspring are produced
than can survive
Genetic Variation
__________________there is variation within the traits
in a population; some individuals in a population are better
able to survive than others because of their traits
Struggle to survive the environment does not have
__________________enough food, water, and other resources to support every
individual; there is going to be competition for survival
within a population and not all individuals will survive to
adulthood
Successful reproduction The individuals with the favorable
_______________________adaptations will be more successful at producing offspring
and eventually will take over the population
How has evolutionary theory changed since Darwin?
Darwin didn’t know anything about genes. Now we know
that it is changes in the DNA or mutations that cause the
variation in a population.
mutation
________________ - changes in the DNA
mutations lead to the variations or differences in the
genes which then cause differences in traits
sometimes those differences can cause an
individual in the population to survive better.
Evidence supporting the theory of evolution
Fossil record
1. _______________
fossils – solidified remains or imprints of
__________
once-living organisms
Using fossils, scientists have constructed a fossil record or
historical sequence of life.
Gaps exist but they are being
filled in all time.
Vestigial structures
2. ___________________
Vestigial structures are remnants of
structures that had a useful role at one time
but no longer do.
The presence of these structures suggests
that the organism evolved from another life
form where that structure played a
more important role.
examples:
remnants of hind-limb bones in whales and some snakes
_________________________________________________
tailbone in humans
_________________________________________________
3. comparing organisms that are alive today
Skeletal structures
a. ___________________
– bone structures of mammals
are very similar suggesting a common origin
(see figure 9 on .156 in your textbook)
DNA – all living organisms have the same genetic
b. ________
material
organisms that are more closely related have DNA that is
more similar
98
example: human and chimp genes are ~ _________%
identical
70
human and mouse genes are ~ _________%
identical
cells
c. _________
– cells are the basic unit of all life;
all living organisms start from a single cell